Liquid oxygen explosive and method of preparing same



tates Patent Lester P. Barlow, Stamford, Conn.,. assignor to Glmite Corporation, Stamford, Conn-.,. a corporation of Connecticut No Drawing. Applicationzlanuary- 31 1955, Serial No. 484,863

4 Claims. clzsz -r The present invention relates to liquid oxygenexplo sives and more particularly'to' liquid oxygen explosives which may be-safely handled andiwhi'ch havehigh brisance. and high power.

Liquid oxygen explosives are composed of liquidoxygen and a combustible-material and have" long been known as extremely powerful explosives; Liquid oxygen has been used in various forms from liquid aircontaining about oxygen to substantially pure liquid oxygen and various combustible materials have been used-includ ing wood pulp, cotton, lamp black, carbon, hyd'rocarbons, metal powders, sulphur and the like.

The liquid oxygen explosives ofthe prior art have been characterized by certain serious and well recognized defects. The principal defect hasbeen the sensitivity ofthe explosives to fire and/or impact so thatthese explosives have been extremely dangerous and have caused numerous accidents. Efiorts have been made tor-overcome thisextreme sensitivity by treatingor fireproofingf the combustible material but despite these effortsliquid oxygenexplosives are not recognized aspermissible? explosives by'the U. S; Bureau of Mines.

Efforts to increase the speed or'brisance of liquidoxy gen explosives have also met with only limited success. Abrasive material's suchas sand or Carborundum have been added to the explosive in amounts of'2-5' to 50% or more. While the addition of abrasives increases the brisance, the abrasives decrease the total power of the explosive because they are inert and in effect, dilute the explosive.

I have found that liquid oxygen explosives can be made which are safe to handle, being in many casesless sensitive toaccidental detonation than conventional explosives, and that the brisance can be increased without substantial loss of power. One of the principal objects of the present invention is therefore to produce a liquid oxygen explosive which is safeto' handle and which is characterized by high brisance and'power.

Another object of the present" invention is to provide a liquid oxygen explosive in which the combustible material is fire'retardant and abrasive.

Another object of the present invention, is to provide a liquid oxygen explosive which can be detonated only by the most powerful of commercial detonators such as Primacord'.

Another object of the. present. invention is to provide a new and improved combustible material for use in: liquid oxygemexplosives. 1

These and other objects: and advantages. reside incerta'in. novel features: of composition andirr step's;andi treatments; as will hereinafter be more fullyset forth andrpointedout in the appended claims.

According". to the present invention I use activated or adsorbent carbon which may be derived from various sources especially vegetable or decomposed vegetable matter.. The carbon should be free or substantially free from hydrophobic material such as hydrocarbons and should be entirely free of low temperature volatile materials: or

low ignition point impurities. One suitable form of carbon is the so-called lignin carbon, a by-product of the paper industry. Another suitable form of activated carban isthatderived from lignitecoal. It is to be understoodhowever that any of the various known forms of activated, adsorbent carbon can be used.

The particle size of the carbon is not critical but when the particles of carbon are small, the mass of particles absorbs more liquid oxygen. Since the particles are also activated, the oxygen is also adsorbed into'each particle. I prefer to use particles of about 150 to 250 mesh with an average particle size ofabout 200 mesh.

The activated carbon particles are treated with a fire retarding agent such as phosphoric acid or phosphoric acid salts such as ammonium acid' phosphate to make the particles fire retardant.

As will be later explained, the carbon-phosphoric acid ratio by weight is critical and the carbon and acid are weighed to obtain the proper ratio. When commercial acid (about to H3PO4) is used, the amount is. corrected to obtain the proper weight of pure acid. Water is then added to the acid' and thecarbon and acid are thoroughly mixed in a thin mud orslurry. The amount of water is not critical so longas there is enough to thoroughly saturate the carbon.

The slurry is then heated to drive off the water and agitation is preferably continued to prevent caking or burning. This heating is usually done at temperatures of' about 250 F. to 450 F. so that the product will be thoroughly dried without burning.

I prefer to mix the slurry in a tub or vet to insure thorough saturation of the carbon and penetration of the carbon by the acid. The drying may be done in the same tub or vat or in various other ways such as in a rotary kiln or in a belt drier.

The exact physical and chemical action which takes place when the activated carbon is treated with the aqueous solution of phosphoric acid and then dried is not entirely clear. Apparently the carbon adsorbs some of the phosphoric acid and possibly impurities in the carbon react with the phosphoric acid to produce complex phosphates. When the carbon is heated and the moisture driven 01f, apparently the phosphoric acid and some of the reaction products aredeposited throughout the porous body of eachparticle carbon. The heating may also decompose some of the phosphoric acid compound to form phosphoric anhydrid'e (P205) or the like.

Regardless of the nature of the physical or chemical changes involved, the treated product is quite difierent from the original and has the characteristics of a crystalloidL The treated carbon crystalloid has a harsh, gritty feel and ishard and abrasive. Apparently some insoluble compounds are formed because even prolonged soaking in water does not substantially change the harsh abrasive character.

I have found that when the carbon contains more than about 18% phosphoric acid by weight, it is sofire retardant that a. liquid oxygen cartridge made with such carbon cannot be. detonated even withPrimacord. Rifle bullets can be fired through the-cartridge and Primacord, fulminate of mercury, blasting caps and other detonators are unable to detonate it. Below about 18% acid, Primacordi will detonate the explosive and below about 2 1.41% acid, fulminat'e of mercury blasting capswill detonate it. When the carbon. crystalloid contains from about 2: /2l% to about 18% acid, the resulting explosive can be detonated only by the most: powerful detonators and; will be insensitive not; only to the normal causes of accidental. detonation but even to the less powerful commercial detonators.

As. the amount of, acid is: increased from 2%%, to 18%, the resulting crystalloid becomes harder and more abrasive. At 2V2%, the carbon crystalloid is still somewhat soft like the untreated activated carbon. The phosphoric acid is not combustible so that it acts to dilute the explosive and reduce its total power. I therefore prefer to use about 8% to 10% phosphoric acid by weight and the crystalloid carbon is then not only extremely safe but is sutficiently hard and abrasive to provide brisance which has heretofore been obtainable only by adding large quantities of inert sand or other abrasive.

To obtain comparable safety and brisance with prior art methods would result in a serious loss of total power.

Holderer Patents Nos. 1,960,907 and 2,119,050 describe methods of treating carbon for liquid oxygen explosives with water and acid. In Patent 2,119,050, 20% of the aqueous solution is left in the carbon and in Patent 1,960,907, water in the amount of 15% to 25% and even up to 32% is left in the carbon in addition to the acid. Commercial so-called fireproofed explosives made in this way contain about 10% acid and about 17% water (see Bureau of Mines Bulletin 472 (1949) entitled Safety and Performance Characteristics of Liquid-Oxygen Explosives p. 84). To increase brisance in liquid oxygen explosives 25 to 50% inert sand is added (Bureau of Mines Bulletin 472 p. 26). A cartridge which is fire retardant and has high brisance would thus contain from 52% to 77% inert material (phosphoric acid, water and sand) and only 23% to 48% combustible material capable of entering into an explosion. My preferred carbon crystalloid contains 90% to 92% combustible material and since the crystalloid itselfis abrasive, the brisance is very high. v

This fact is demonstrated by independent tests. The U. S. Bureau of Mines made tests on a commercial liquid oxygen explosive produced by Airrnite Corp. and employing lampblack as a combustible. In Bureau of Mines Report of Investigations 4918 (June 1953), the powder factor of the Airmite explosive is given as two pounds per cubic yard of taconite rock. In a report of an explosion made with a liquid oxygen explosive containing the carbon crystalloid of the present invention, the Oliver Iron Mining Division of the United States Steel Corporation found the powder factor of the explosive to be 0.86 pound per cubic yard of taconite rock.

According to the present invention the treated carbon may be packed in bags and these bags soaked in liquid oxygen. Since liquid oxygen boils at a very low temperature (about -183 C.), this soaking should be done at or near the place where the explosive is to be used. Of course, the liquid oxygen and treated carbon can also be mixed in bulk or in any other suitable way. One very safe and satisfactory way of loading liquid oxygen ex plosives into blast holes is described and claimed in my copending application Serial No. 456,099 filed September 15, 1954 entitled Explosive Composition and Process.

The stoichiometric liquid oxygen-carbon ratio is 2.66 parts by weight of oxygen to 1 part of treated carbon but for complete combustion and maximum power it is preferable to use a small excess of oxygen. However, oxygen-carbon ratios from about 2 to 1 to about to 1 are satisfactory and when bags of carbon are soaked with liquid oxygen, there is frequently less than 2 parts of oxygen for each part of carbon by the time the bag is later detonated in the hole.

For one blast, an aqueous solution of phosphoric acid was added to lignin carbon until the amount of phosphoric acid present was equal to of the carbon by weight. Sufficient water was used or added until the mass formed a fluid mud or slurry and this slurry was thoroughly mixed. The slurry was then heated over a gas flame in an open metal vat until the treated carbon was substantially completely dried and was agitated during drying. At the start of the drying, the temperature was about 250 F. The temperature rose to about 450 F. as the drying progressed but the temperature was not permitted to exceed 450 F. to prevent possible burning.

The carbon so treated was placed in fireproofed canvas bags about 22" long and 9 /2 in diameter and soaked in liquid oxygen. These bags of carbon soaked up 2.2 parts by weight of liquid oxygen for each part of treated carbon and, due to vaporization of the oxygen, the bags of treated carbon may contain only about 1.8 parts by weight of oxygen for each part of carbon when detonated.

The liquid oxygen explosives containing carbon so treated was tested and could be ignited but not detonated by a burning newspaper and was not affected by rifle fire using .30 caliber soft nose bullets. The explosive did detonate with a Primacord detonator.

The explosive compositions of the present invention are particularly useful in mining operations where it is desired to employ an explosive having tremendous power to open up a seam of coal or other valuable mineral in solid rock formations or the like. Open pit strip mining operations are also greatly facilitated by the use of the explosive compositions of the present invention. One particularly important application of the present invention is in the mining of taconite.

Taconite is an iron ore and as the higher grade ores become exhausted, taconite, which is found in the United States in almost inexhaustible quantities, will be an increasingly important source of iron. Processes for recovering iron from taconite are known but due to the lack of an inexpensive, high power, high speed, safe explosive, the expense of blasting particularly secondary blasting, has hindered the commercial production of iron from taconite. Because of its high power and brisance, the explosive of the present invention successfully blasts taconite and causes such high fragmentation that secondary blasting is usually unnecessary.

Various modifications can of course be made without departing from the spirit of the present invention or the scope of the appended claims. Various crystalloidforming, fire-retardant materials and activated carbons from various sources may be used.

This application is a continuation-in-part of application Serial No. 466,652 filed November 3, 1954 entitled Explosive which was a continuation-in-part of application Serial No. 351,035 filed April 24, 1953, now abandoned entitled Explosive Material.

I claim:

1. The method of preparing a liquid oxygen explosive which comprises mixing finely divided activated carbon with an aqueous phosphoric acid solution containing the phosphoric acid in an amount equal to about 2 /z% to about 18% by weight of the carbon and sufficient water to form a fluid mud substantially completely drying the carbon and soaking the dried carbon with liquid oxygen.

2. The method of preparing a liquid oxygen explosive as defined in claim 1 in which the treated carbon is dried at a temperature between 250 F. and about 450 F.

3. A liquid oxygen explosive comprising from about 2 to about 5 parts of liquid oxygen and 1 part activated carbon which has been mixed with an aqueous phosphoric acid solution containing phosphoric acid in an amount equal to from about 2 /2% to about 18% of the weight of carbon and suflicient water to form a fluid mud and which has been substantially completely dried.

4. A liquid oxygen explosive comprising from about 2 to about 5 parts of liquid oxygen and 1 part activated carbon which has been mixed with an aqueous phosphoric acid solution containing phosphoric acid in an amount equal to from about 8% to about 10% of the weight of carbon and sutficient water to form a fluid mud and which has been substantially completely dried.

References Cited in the file of this patent UNITED STATES PATENTS 1,473,994 Lisse Nov. 13, 1923 2,119,050 Holderer May 31, 1938 2,347,955 Korpi May 2, 1944 

1. THE METHOD OF PREPARING A LIQUID OXYGEN EXPLOSIVE WHICH COMPRISES MIXING FINELY DIVIDED ACTIVATED CARBON WITH AN AQUEOUS PHOSPHORIC ACID SOLUTION CONTAINING THE PHOSPHORIC ACID IN AN AMOUNT EQUAL TO ABOUT 2 1/2% TO ABOUT 18% BY WEIGHT OF THE CARBON AND SUFFICIENT WATER TO FORM A FLUID MUD SUBSTANTIALLY COMPLETELY DRYING THE CARBON AND SAOKING THE DRIED CARBON WITH LIQUID OXYGEN,
 3. A LIQUID OXYGEN EXPLOSIVE COMPRISING FROM ABOUT 2 TO ABOUT 5 PARTS OF LIQUID OXYGEN AND 1 PART ACTIVATED CARBON WHICH HAS BEEN MIXED WITH AN AQUEOUS PHOSPHORIC ACID SOLUTION CONTAINING PHOSPHORIC ACID IN AN AMOUNT EQUAL TO FROM ABOUT 2 1/2% TO ABOUT 18% OF THE WEIGHT OF CARBON AND SUFFICIENT WATER TO FORM A FLUID MUD AND WHICH HAS BEEN SUBSTANTIALLY COMPLETELY DRIED. 